Molecular Script Add-on: Why does this simple particle system blow up?
Issue comes from particles self collision (so boundaries).
In your case if you Display as Circles, you can see they are overlapping, set Render size to 0.02. Particles stops to explode.


To see particle's collision boundaries switch Viewport display &gt; Display as Rendered to Circle.
Adjust Size value, so circles doesn't overlap.
The same value set in Render &gt; Render as Object &gt; Scale panel.
Then you can switch back Display &gt; Display as Rendered.
Scale object (Sphere) in 3Dview (Object or Edit mode) to desired size.


What matters - Render Scale (viewport size is only for reference)
What confuse - Object Scale in 3D view does not affect self collision
The goal is to keep not overlapped &quot;Display as Circles&quot; with the same value for &quot;Render as Object&quot; ... Than if you scale object (Sphere) in 3Dview via Object mode or Edit mode doesn't matter. A size of object doesn't matter here, object can overlap each other or be a micro, its size doesn't affect behaviour of particles.
Render Scale 0.05

Render Scale 0.1



To see real boundary with Rendered as Object - add a new Sphere (by default Scale 1 / Dimension 2) and set Render Scale to 0.02, same set for selected Sphere in 3Dview Properties &gt; Item &gt; Transform &gt; Scale. To see it right, uncheck in Particles Properties &gt; Render &gt; Object &gt;  Object Scale. Now you can change only Render Scale value and have a control over real boundary at the same time (don't change Scale in 3D view from now).


Note: Object Scale means - use object scale value on top of particle scale. If particle will be size 2 and object scale 0.5 rendered particle (Sphere) will be size 1, but size of collision boundary stay 2. And &quot;Render Scale&quot; value matters :)